docs: def save_trailer(self, tocpos):
          """Save the trailer to disk.
  
             CArchives can be opened from the end - the trailer points
             back to the start. """
          totallen = tocpos + self.toclen + self.TRLLEN
          pyvers = sys.version_info[0]*10 + sys.version_info[1]
          trl = struct.pack(self.TRLSTRUCT, self.MAGIC, totallen,
                            tocpos, self.toclen, pyvers)
          self.lib.write(trl)